Abstract

Harpagophytum procumbens, commonly known as Devil’s Claw, is indigenous to southern Africa, and extracts of the
tubers have been used for centuries in the treatment of a variety of inflammatory disorders. Its major active components,
harpagoside (1), harpagide (2), 8-coumaroylharpagide (3), and verbascoside (4), are believed to interact either
synergistically or antagonistically in modulating the enzymes responsible for inducing inflammation, although this has not been probed hitherto. In the current work, the ability of these compounds to inhibit the expression of COX-2 following
administration to freshly excised porcine skin has been investigated. An ethanol-soluble extract of H. procumbens tubers
and two of the pure compounds tested showed promising activity in Western blotting and immunocytochemical assays,
with harpagoside (1) and 8-coumaroylharpagide (3) exhibiting greater reductions in COX-2 expression than verbascoside
(4). Harpagide (2) caused a significant increase in the levels of COX-2 expression after 6 h of topical application. The
data suggest that the efficacy of H. procumbens is dependent upon the ratios of compounds 1–4 present, which is
inconsistent with some current official monograph specifications based solely on harpagoside (1) content.